# TZ(5)

## NAME

         TZ - Time zone environment variable

## SYNOPSIS

         TZ=zone[-]offset[dst[offset][,start[/time],end[/time]]]

## DESCRIPTION

         The TZ environment variable tells functions such as the  ctime(3)  family
         and  programs  like  date what the time zone and daylight saving rule is.
         The value of TZ has the POSIX standardized form shown  in  the  synopsis.
         This  form  specifies  the  zone  names,  offsets  from GMT, and daylight
         savings changeover times for at least the current year.

         zone A three or more letter name for the time  zone  in  normal  (winter)
              time.

         [-]offset
              A signed time telling the offset of the  time  zone  westwards  from
              Greenwich.   The  time  has  the form hh[:mm[:ss]] with a one of two
              digit hour, and optional two digit minutes and seconds.

         dst  The name of the time zone when daylight savings is  in  effect.   It
              may be followed by an offset telling how big the clock correction is
              other than the default of 1 hour.

         start/time,end/time
              Specifies the start and end of the  daylight  savings  period.   The
              start  and  end  fields  indicate on what day the changeover occurs.
              They must be in one of the following formats:

              Jn   The Julian day n (1 <= n <= 365) ignoring leap days, i.e. there
                   is no February 29.

              n    The zero-based Julian day (0 <= n <= 365).  Leap days  are  not
                   ignored.

              Mm.n.d
                   This indicates month m, the n-th occurrence of day d (1 <= m <=
                   12,  1  <= n <= 5, 0 <= d <= 6, 0=Sunday).  The 5-th occurrence
                   means the last occurrence of that day in a month.  So M4.1.0 is
                   the  first  Sunday  in  April,  M9.5.0  is  the  last Sunday in
                   September.

              The time field indicates the time the changeover occurs on the given
              day.

## EXAMPLES

         Greenwich Mean Time:

              TZ=GMT0

         Middle European Time, 1 hour east from Greenwich, daylight savings starts
         on  the  last  Sunday  in  March  at  2 AM and ends on the last Sunday in
         October at 3 AM:

              TZ='MET-1MET DST,M3.5.0/2,M10.5.0/3'

         British time, daylight savings starts and ends at the same moment as MET,
         but in an earlier time zone:

              TZ=GMT0BST,M3.5.0/1,M10.5.0/2

         The eastern european time zones also have the  changeovers  at  the  same
         absolute time as British time and MET.

         U.S. Eastern Standard Time, 5 hours west from Greenwich, daylight savings
         starts  on  the first Sunday in April at 2 AM and ends on the last Sunday
         in October at 2 AM:

              TZ=EST5EDT,M4.1.0/2,M10.5.0/2

         It shouldn't surprise  you  that  daylight  savings  in  New  Zealand  is
         observed in the months opposite from the previous examples.  It starts on
         the first Sunday in October at 2 AM and ends on the third Sunday in March
         at 3 AM:

              TZ=NZST-12NZDT,M10.1.0/2,M3.3.0/3

## SEE ALSO

         readclock(8), date(1).

## BUGS

         You may have noticed that many fields are optional.   Do  no  omit  them,
         because  the defaults are bogus.  If you need daylight savings then fully
         specify the changeovers.

         West is negative, east is positive, ask any sailor.

## AUTHOR

         Kees J. Bot (kjb@cs.vu.nl)